The environment contains a large number of toxins that adversely affect the health of humans. These toxins range from inorganic compounds such as lead and asbestos to microbial toxins such as afiatoxin and staphylococcalenterotoxins involved in food poisoning. Environmental bacteria in particular represent a large reservoir of agents capable of producing diverse toxins with the potential to affect human health. Genome sequencing has nicely defined the core set of invariant chromosomal genes carried by many of these organisms, but a substantial amount of genetic information varies from strain to strain in the form of genomic islands and remains undefined. These genomic islands may represent 10-20% of the total genetic information carried by some environmental bacteria. Many of these genomic islands encode toxins and other virulence determinants that have the potential to adversely affect human health. Pseudomonas aeruginosa is an environmentally ubiquitous bacterium that causes disease in both plants and animals, including humans. Humans frequently become colonized with P. aeruginosa following ingestion of contaminated environmental sources such as food or water. Although this colonization is typically unapparent and short-lived, in patients who are compromised in some way, P. aeruginosa frequently emerges to cause life-threatening infections. In fact, P. aeruginosa is the leading cause of pneumonia in mechanically ventilated patients and is associated with mortality rates as high as 70%. To cause such severe disease, P. aeruginosa produces a plethora of toxins, but the true breadth of virulence factors produced by this bacterium is unclear. We hypothesize that novel genomic islands of the environmental bacterium P. aeruginosa encode a number of previously uncharacterized virulence factors. In this application, we propose to employ a targeted strategy to identify novel genomic islands in P. aeruginosa. The islands will then be sequenced, and the genes they carry that affect virulence in animals and plants will be identified. It is anticipated that a number of these genes will encode novel toxins or novel export systems that secrete toxins. Successful completion of these aims will identify novel factors produced by the environmental bacterium P. aeruginosa that have the potential to adversely affect human health. Relevance: Pseudomonas aeruginosa is a common environmental bacterium that produces a large number of toxins. We propose to identify additional factors produced by this bacterium that have the potential to harm humans. Identification of these factors will lay the foundation for the development of therapeutic interventions that block the action of these factors and thereby improve human health.